Good guide... just to share a little, since most are shooting digital, i think it's best if your shutter speed is higher than 1/50.
The guide for shake-free photo is 1/focal length of your lens. i.e. using 105mm, then 1/100 s will be good. 1/125 s will be safer. Of course, if you have VR or IS function on your lens/camera, on it as it will help.
Next, i know some will say you can fix the speed fast enough. The easiest way to do it is to set your ISO higher. Sure, it may be a little grainier but it's usually ok for our purpose of sharing and showcasing our fish/corals. It's always better to be grainier than to be blur.